1 files changed, 11 insertions, 15 deletions
diff --git a/ext/js/dom/panel-element.js b/ext/js/dom/panel-element.js
index 9c1289d7..0f2801e6 100644
--- a/ext/js/dom/panel-element.js
+++ b/ext/js/dom/panel-element.js
@@ -89,16 +89,14 @@ export class PanelElement extends EventDispatcher {
      * @param {(details: import('core').EventArgument<import('panel-element').Events, TName>) => void} callback
      */
     on(eventName, callback) {
-        if (eventName === 'visibilityChanged') {
-            if (this._mutationObserver === null) {
-                this._visible = this.isVisible();
-                this._mutationObserver = new MutationObserver(this._onMutation.bind(this));
-                this._mutationObserver.observe(this._node, {
-                    attributes: true,
-                    attributeFilter: ['hidden'],
-                    attributeOldValue: true
-                });
-            }
+        if (eventName === 'visibilityChanged' && this._mutationObserver === null) {
+            this._visible = this.isVisible();
+            this._mutationObserver = new MutationObserver(this._onMutation.bind(this));
+            this._mutationObserver.observe(this._node, {
+                attributes: true,
+                attributeFilter: ['hidden'],
+                attributeOldValue: true
+            });
         }
         super.on(eventName, callback);
     }
@@ -111,11 +109,9 @@ export class PanelElement extends EventDispatcher {
      */
     off(eventName, callback) {
         const result = super.off(eventName, callback);
-        if (eventName === 'visibilityChanged' && !this.hasListeners(eventName)) {
-            if (this._mutationObserver !== null) {
-                this._mutationObserver.disconnect();
-                this._mutationObserver = null;
-            }
+        if (eventName === 'visibilityChanged' && !this.hasListeners(eventName) && this._mutationObserver !== null) {
+            this._mutationObserver.disconnect();
+            this._mutationObserver = null;
         }
         return result;
     }